Head Temperature top five, *** Give me the top five reasons head temps run high ***** Options

[wndsnd]

Is the thermostat installed and what is the position of your cooling flaps?

The t stat is there and the flaps are open

[wndsnd]

I have the AEM Paul but I noticed when car is really cold it blacks out.

[ThePaintedMan]

A couple things here, IMHO:

1) What kind of CHT gauge are you using? If it's a VDO type, then it's non-compensating type. Up where you guys are, you've been having cold weather, which means that it likely is reading quite a few degrees higher than the actual CHT is. Read more here:

http://www.ratwell.com/technical/VDOGauges.html

2) Timing is probably one of the biggest drivers of CHT temps, especially under load. However, you know your stuff and as long as you're pretty confident you have it set correctly, you're probably pretty close and can rule that out as you main concern.

3) Jetting, especially under load. If you've got the temps way down, then you were probably way lean previously. What mains and idle jets are in it now, and what size engine are we talking about?

4) Sync of the carbs. If one carb is open more than the other, that side of the engine is doing far more work. If that happens to be the side you have the CHT lead on, then the higher temps you're seeing are a good indication that the other side might not be pulling it's weight. Verify your sync tomorrow before you get on the road with the gauge (you have a synchrometer, correct?) Might even try checking it at several different RPMS - idle, 2k and 3k.

5) Valves - if you've got a tight valve lash on the #3 cylinder (where your CHT lead should be), especially an exhaust, you're not letting the valve do it's secondary, but important role of sinking heat away from the head. Check your valve lash adjustment before you start it up in the morning. Keep it on the loose side instead of tight if you're concerned, especially on the exhaust valves.

When in doubt, run it pig rich with jets if you're just trying to get to Chris' shop. Doing it for too long can be harmful, but if it's far too lean, you're risking really high temps which could do more damage quicker. Also, if you being to see the temps spike, slow down a little and downshift. The less "lugging" you put the engine through, the lower the temps should be. After that, let Chris help you figure the rest out - I learned a lot from him, and he is truly one of the Obi-Wans here. (IMG:style_emoticons/default/beerchug.gif)

[Jake Raby]

How hot?

You don't want to know. According to Raby the engine should have self destructed by now.

If the CHTs are truly that high and have been for a while you should have symptoms... The first symptom of high CHT is tight valves.

If you don't have symptoms and it hasn't scattered yet, I'd question the validity of the data.

CHT is fairly unaffected by ambient temps, while oil temp is heavily impacted by ambient temps. Of course, non-temperature compensated CHT gauges can send false data in cold temperatures.

This post has been edited by Jake Raby: Nov 28 2013, 10:00 PM

[wndsnd]

Thanks George

That is all good information and food for thought. I will not have time to do the checks you mention before I go as we are leavin g very early. However I did get the temps down I thiink enough for the drive.

I am having Chris install his cable linkage and tune the carbs so I am hoping to have a new car when it comes back.

John

[wndsnd]

How hot?

You don't want to know. According to Raby the engine should have self destructed by now.

If the CHTs are truly that high and have been for a while you should have symptoms... The first symptom of high CHT is tight valves.

If you don't have symptoms and it hasn't scattered yet, I'd question the validity of the data.

CHT is fairly unaffected by ambient temps, while oil temp is heavily impacted by ambient temps. Of course, non-temperature compensated CHT gauges can send false data in cold temperatures.

Thanks Jake,

I did not put too many miles on it as I was watching it closely and followed your advice about letting itgo through it natural cooling cycle and not cooling too quickly.

It has been cold here but with the change in jetting I saw an immediate impro vement with the same ambient temps.

[r_towle]

I may sort of be on the way to chaises if you want to drop by and retune it.

Around all weekend.

Rich

[gothspeed]

Recheck the valve adjustment, this is sometimes a symptom of valves not 'seating' all the way closed ..... in other words too tight. (IMG:style_emoticons/default/popcorn[1].gif)

Also, is the camshaft timed correctly?

[Rand]

Some input from my experience.... In my testing, advanced timing raises head temps but not oil temps. Retarded timing raises oil temps but not head temps. Just some real life results to throw into the mix. This is assuming a clean system.

No matter what, you have to have a good baseline, meaning your valve adjusts have to be ON and any other random factors need to be clear, including rats nests in the airflow and overload of gunk anywhere. Get it clean, time it right..... Report back.

[gothspeed]

Some input from my experience.... In my testing, advanced timing raises head temps but not oil temps. Retarded timing raises oil temps but not head temps. Just some real life results to throw into the mix. This is assuming a clean system.

No matter what, you have to have a good baseline, meaning your valve adjusts have to be ON and any other random factors need to be clear, including rats nests in the airflow and overload of gunk anywhere. Get it clean, time it right..... Report back.

Good point! One must make sure there is nothing blocking the cooling fan! (IMG:style_emoticons/default/smash.gif)

[bulitt]

Timing
AF ratio

1. Too advanced, or too retarded? I would guess retarded.
2. Too lean? Idle fuel adjusts are two turns out. That should be plenty unless jetting is wrong.

Advanced= very hot and chance of detonation
Retarded= fuel incomplete burn in cylinder then the burn continues past the valve into the exhaust. Can make my headers glow cherry red by backing off on the timing.

Higher ompression increases heat.
Low octane fuel increase chance of detonation- more heat
High octane fuel packs more energy= more heat

[wndsnd]

Well I ran it rich and it made the 2 1/2 hour trip to Racer Chris with no events.

It is in good hands now.

[adam415]

A rich condition will not make your motor-any part of it hot. if anything at all it will run cooler from the unburned fuel cooling your piston and cylinder. this is non as cylinder wash. also retarding your timing will not create more heat in any situation. as far as your A/F meter is concerned, 14.7 is what is called lamda or known as '1" the middle point between good MPG and ok power. if your metter is swinging all the way to 18 that is way to lean and makes heat VERY fast. 8 or 9 is the lowest with gasoline you could drive around on and around 12-13 is going to make the best power.
i would set your timing to what the manual calls for and then rejet and tune you're carbs. and see where the temp lands then.

[adam415]

Timing
AF ratio

1. Too advanced, or too retarded? I would guess retarded.
2. Too lean? Idle fuel adjusts are two turns out. That should be plenty unless jetting is wrong.

Advanced= very hot and chance of detonation
Retarded= fuel incomplete burn in cylinder then the burn continues past the valve into the exhaust. Can make my headers glow cherry red by backing off on the timing.

Higher ompression increases heat.
Low octane fuel increase chance of detonation- more heat
High octane fuel packs more energy= more heat

high octane fuel dose not have more energy, it is just more resistant to nock and detonating.